1. Field of the Invention
This invention relates to a drawbar construction for a semitrailer which can be connected to a pulling vehicle and is partly supported thereby, e.g. for a tractor connected trailer. According to the invention it is possible also in the case of light tractors and trailers to achieve a vehicle combination which is laterally stable, whereby a laterally extending lifting device, e.g. a crane mounted on the trailer can be used without any additional stud devices. The drawbar construction is applicable especially for timber transporting cross-country vehicles.
2. Description of the Prior Art
For the forest transportation of timber, almost solely different mechanical transport units are used nowadays. This unit usually comprises a lifting device, by means of which the trees felled and delimbed and possibly also cut into predetermined lengths in the forest are loaded onto the transport unit. The lifting device comprises gripping means extending laterally from the transport unit, by means of which gripping means the logs spread on the ground or stacked can be lifted up into the load space of the transport unit.
The difficult working conditions of these equipments have led to the use of large machine units which aim to a large transportation capacity and a good durability also under unfavourable conditions. However, big units have the disadvantage of damaging the terrain, trees and seedlings. During thaw weather and mild winters it may be difficult to use these large and heavy machines on badly supporting ground, as on unfrozen marsh.
In order to avoid the aforementioned difficulties, light transport units have been used, comprising light pulling vehicles provided with endless tracks or the like and suitable for moving over such terrain, connected to suitable semitrailers. Agricultural tractors have also been used as relatively light pulling vehicles for forest transportation.
A disadvantage of these structurally light combinations of pulling vehicle and trailer has been their poor lateral stability during loading. A crane, which is usually mounted on the pulling vehicle, causes a considerable unbalance when a load is lifted from the side up onto the trailer. The unbalance can make the whole transport unit or a part thereof tip over. In the beginning of loading, moreover, the trailer is relatively light and cannot function as a steady support for the lifting means. The crane can be provided with auxiliary studs but the use of such studs in terrain is a complicated and time consuming procedure. The use of extending studs also limits the movement of the vehicle over the terrain. In the case of an agricultural tractor, the lifting device has to be removable, which naturally causes additional expenses and work.